The invention relates generally to an apparatus for connecting a graphite electrode to a permanent electrode in an electric furnace, the graphite electrode and the permanent electrode together forming the actual electrode of the electric furnace. The electrode can therefore also be referred to as a composite electrode.
Conventional electric furnaces use graphite electrodes which comprise at least two portions which are screwed together in axial succession by means of screw nipples comprising carbon or graphite. The electrodes pass upwardly through the cover of the furnace and are suitably supported by a holding arrangement disposed above the cover of the furnace. The electrodes can be moved downwardly out of the holding arrangement into the furnace with a stepwise motion, as the electrodes are burnt away.
After the electrode has been reduced in length in this manner, a fresh electrode portion must be screwed on to the upper end of the graphite electrode which is held in a clamping device, the screw connection being formed by means of a carbon or graphite nipple which is screwed on to the graphite electrode. As a conventional portion, as referred to above, of an electrode comprised of graphite, carbon or the like, is several meters in length, for use in the electric furnaces which are conventionally employed nowadays, and is of considerable weight, various forms of nipple connecting arrangements have already been proposed for carrying out the above-indicated operation of connecting the graphite electrode and the fresh electrode portion by means of a nipple connection, from above (see for example DE-A No 23 12 968), such devices being used to screw a fresh electrode portion or section to the graphite electrode which is held in a clamped condition, above the electric furnace.
However, an unsatisfactory consideration in the above-indicated conventional furnaces is that the electrodes which are made up of a number of electrode portions or sections tend to suffer comparatively severely from erosion and breakage, and electrode breakages cause not inconsiderable amounts of material and time to be lost. For that reason, it has been suggested in fairly recent times (see for example DE-A No 27 39 483) that the end of the electrode which projects upwardly out of the electric furnace and which is held in the support arrangement and which is connected at the top to a current source should be made in the form of a permanent or continuous electrode comprising copper or a metal which is a similarly good conductor, with the permanent or continuous electrode being cooled by a coolant, for example a water circuit. The term permanent electrode is used in this specification to indicate an arrangement of the kind just described. In such an arrangement, the lower end of the permanent electrode, which projects into the electric furnace, is in the form of a screw nipple so that a portion or section of a conventional graphite electride then only needs to be screwed to the screw nipple to make up an electrode. The mere fact that the upper portion or section of the electrode which is gripped in the support device is of metal results in a substantial reduction in the risk of erosion and breakage. However, there is the disadvantage in comparison with the previously conventional graphite electrodes that the operation of connecting the graphite electrode to the permanent electrode by means of a nipple connecting means can no longer be carried out from above, so that the known nipple connecting devices also cannot be used. As moreover the lower end of the electrode retains its very high temperatures during the short period of time involved in changing a furnace charge, hitherto no possibility has been seen of connecting a fresh graphite electrode section to a permanent electrode which has been in use immediately before the connecting operation, for example during the short period of time involved in changing a furnace charge. On the contrary, the permanent electrode which had been in use prior to the change of graphite electrode section had to be disconnected from the current and coolant connections, and removed from the support arrangement, and a second permanent electrode which, while cold, had already been provided with a graphite electrode connected thereto by a nipple connection had to be fitted into the support means to be clamped thereby, and connected to the coolant circuit and the current supply. The permanent electrode which had been used previously could then be provided with a fresh electrode section after it had cooled down, during the next period of operation of the furnace, and the remaining portion of electrode which had been previously removed from the permanent electrode and which had not yet been fully consumed could then be re-connected to the fresh electrode portion, at the lower end thereof, by means of a conventional screw nipple comprising graphite. Even if simple devices are available for fitting and removing electrode portions to and from the permanent electrode it has cooled, nonetheless the above-described operation involves disadvantages which run counter to and detract from the advantage of using the permanent electrode.